Non-invasive assessment of the haemodynamic significance of coronary stenosis using fusion of cardiac computed tomography and 3D echocardiography

Abstract

Aims: Abnormal computed tomography coronary angiography (CTCA) often leads to stress testing to determine haemodynamic significance of stenosis. We hypothesized that instead, this could be achieved by fusion imaging of the coronary anatomy with 3D echocardiography (3DE)-derived resting myocardial deformation.

Methods and results: We developed fusion software that creates combined 3D displays of the coronary arteries with colour maps of longitudinal strain and tested it in 28 patients with chest pain, referred for CTCA (256 Philips scanner) who underwent 3DE (Philips iE33) and regadenoson stress CT. To obtain a reference for stenosis significance, coronaries were also fused with colour maps of stress myocardial perfusion. 3D displays were used to detect stress perfusion defect (SPD) and/or resting strain abnormality (RSA) in each territory. CTCA showed 56 normal arteries, stenosis <50% in 17, and >50% in 8 arteries. Of the 81 coronary territories, SPDs were noted in 20 and RSAs in 29. Of the 59 arteries with no stenosis >50% and no SPDs, considered as normal, 12 (20%) had RSAs. Conversely, with stenosis >50% and SPDs (haemodynamically significant), RSAs were considerably more frequent (5/6 = 83%). Overall, resting strain and stress perfusion findings were concordant in 64/81 arteries (79% agreement).

Conclusions: Fusion of CTCA and 3DE-derived data allows direct visualization of each coronary artery and strain in its territory. In this feasibility study, resting strain showed good agreement with stress perfusion, indicating that it may be potentially used to assess haemodynamic impact of coronary stenosis, as an alternative to stress testing that entails additional radiation exposure.

Keywords: 3D echocardiography; Cardiovascular CT; Fusion imaging; Myocardial strain; Myocardium perfusion; Vasodilator stress.

Figure 1

Schematic diagram of the study design (see the text for details).

Figure 2

3D segmentation model used for quantitative segmental analysis of myocardial strain. The ventricle was divided into three sections (base, mid-ventricle, and apex), by slicing it perpendicular to its long axis. Each section was then divided into six segments using standard segmentation scheme routinely applied to short-axis views (see text for details), resulting in 18 wedge-shaped 3D myocardial segments.

Figure 3

Example of combined 3D displays obtained in a patient with no significant stenosis. The three snapshots depict (from left to right) the anterior, lateral, and septal views to optimize the visualization of the territories of the left anterior descending (LAD), left circumflex (LCX), and the right coronary (RCA) arteries, respectively. These displays depict fairly uniform perfusion during peak vasodilator stress (top row) and resting strain (bottom row) maps.

Figure 4

Example of combined 3D displays obtained in a patient with a stenosis of >70% in the mid-section of the RCA (right, arrows) and a diffuse calcified plaque in the proximal LAD, resulting in intermediate-grade stenosis of close to 50%. A SPD was noted in the infero-septal view depicted by the blue area in the RCA territory (top right) and was accompanied by a resting strain abnormality depicted by the red-orange-yellow area in the same territory (bottom right). Strain abnormality was noted in the LAD territory (bottom, left), whereas perfusion data were inconclusive (top left).

Figure 5

Example of combined 3D displays obtained in a patient with no significant stenosis and no visible SPDs (top panels), but whose strain map showed resting strain abnormalities in the territories of two arteries: first diagonal branch of the LAD (antero-lateral view, bottom) and the RCA (septal view, bottom).

Figure 6

Effects of segmentation on quantitative analysis of myocardial perfusion. In this patient, proximal LAD stenosis (left, arrow) resulted in a clearly visible perfusion defect, following the course of the coronary artery (blue area underlying the LAD). When segmentation was applied (right), the mid-anteroseptal segment contained part of the perfusion defect, but also portions of the normally perfused myocardium.

Figure 7

Effects of segmentation on quantiative analysis of myocardial strain. In this patient (the same as in Figure 4), resting strain abnormality was noted in the LAD territory (left, orange-yellow area). However, when segmentation was applied (right), this strain abnormality was evenly split between four segments: two mid-ventricular and two apical (anterior and anteroseptal), which also contained portions of myocardium with normal strain (blue areas).